Tyre having a high wear resistance, tread band and elastomeric composition used therein

ABSTRACT

An elastomeric composition includes at least one diene elastomeric polymer; at least one reinforcing filler; from 0.05 phr to 10 phr of zinc oxide; from 0.1 phr to 20 phr of at least one fatty acid amide; and from 0.1 phr to 15 phr of at least one zinc salt of a carboxylic acid of formula R—COOH. R is selected from linear or branched C 1 -C 24  alkyl groups, linear or branched C 2 -C 24  alkenyl groups, C 5 -C 24  cycloalkyl groups, C 6 -C 24  aryl groups, C 7 -C 24  alkylaryl or arylalkyl groups. A tyre for a vehicle wheel includes a carcass structure, belt structure, tread band, and pair of sidewalls. At least one tyre structural element includes a crosslinked elastomeric material obtained by crosslinking the elastomeric composition. The at least one structural element including the crosslinked elastomeric material may be the tread band. A related tyre tread band and crosslinked elastomeric manufactured product are also disclosed.

The present invention relates to a tyre for vehicle wheels, to a treadband and to a crosslinkable elastomeric composition.

More particularly, the present invention relates to a tyre for vehiclewheels comprising at least one structural element made of crosslinkedelastomeric material including at least one fatty acid amide and atleast one zinc salt of a carboxylic acid.

The present invention moreover relates to a tread band including acrosslinkable elastomeric composition comprising at least one fatty acidamide and at least one zinc salt of a carboxylic acid, and also to anelastomeric composition comprising at least one fatty acid amide and atleast one zinc salt of a carboxylic acid.

In the rubber industry, in particular in the industry for production ofvehicle wheel tyres, use of elastomeric compositions is known in whichreinforcing fillers are incorporated into the elastomeric base for thepurpose of improving the features of the crosslinked manufacturedarticle, in particular mechanical properties and abrasion resistance.

Due to its high reinforcing power, carbon black is the most widely usedreinforcing filler. However, carbon black gives the crosslinkedmanufactured article marked hysteresis features, i.e. an increase in theheat dissipated under dynamic conditions which, as known, in the case ofa tyre, gives rise to an increase of the rolling resistance of the tyreitself. This leads about an increase in the vehicle fuel consumptionand, consequently, an increase both in the locomotion costs and in airpollution. An attempt to reduce these negative effects can be made byusing smaller amounts of carbon black and/or a carbon black having areduced surface area. This however, inevitably leads to a reduction inthe reinforcing action which worsen mechanical properties and abrasionresistance of the finished product. On the other hand, when carbon blackis used in an excessive amount, a problem arises in that the elastomericcompositions become excessively hard to cause difficulty in industrialprocessing, the dispersion of carbon black in the elastomericcompositions becomes inferior and, also in this case, a reduction in thereinforcing action is obtained.

To overcome said drawbacks, the so-called “white” reinforcing fillerssuch as gypsum, talc, kaolin, bentonite, titanium dioxide, silicates ofvarious types and, above all, silica, are usually used, in total orpartial replacement for the carbon black. In this connection, referencecan be made to European Patent EP 501,227, for example. However, also inthis case there are a series of drawbacks essentially related to thepoor affinity of silica with respect to the elastomers commonly used inthe production of tyres. Moreover, dispersion of silica in theelastomeric compositions becomes inferior and the high viscosity of thesame cause difficulty in industrial processing.

To obtain a good degree of dispersion of said reinforcing fillers, bothcarbon black and silica, processing aids such as, for example, aromaticoil, are usually added to the elastomeric compositions. In someinstances, however, attemps to include large amounts of oils intoelastomeric compositions result in loss of other desirable propertiessuch as, for example, tensile strength, wear resistance and heatresistance.

Moreover, in the case of silica, to increase affinity of silica for theelastomeric matrix, appropriate coupling agents are currently used suchas, for example, sulphur-containing organosilane products having twodifferent groups: a first group which is able to interact with thesilanol groups present on the silica surface, a second group able topromote interaction with the sulphur-vulcanizable elastomeric polymers.Use of said coupling agents however, limits the maximum temperature thatcan be achieved during the mixing and thermomechanical-workingoperations of the elastomeric compositions, under penalty of anirreversible thermal degradation of the coupling agent. In addition, thehigh cost of said coupling agents adversely affects the cost of thefinished product.

Other attempts have been made in the prior art to improve thedispersability of said reinforcing fillers into the elastomericcompositions.

For example, patent application FR 2,790,478 describes a rubbercomposition comprising 100 part by weight of rubber and at least 20 partby weight of silica and at least an amide-containing compound, aphenolic resin and a hardening agent for said resin. Saidamide-containing compound can be selected from: formamide, acetamide,propionamide, butyramide, capronamide, acid lauric amide, stearamide,succinamide, urea, dimetilurea, benzamide, benzanilide,N-ciclohexylpropionamide, N,N-di(hydroxyethylol)amide, ε-caprolactame,butyranilide, succinimide, and the like. Said rubber composition, thanksto a better dispersion of the silica in the same, is said to give acrosslinked rubber composition having an improved tearing resistance.

U.S. Pat. No. 5,962,562 describes a method for processing a rubbercomposition which comprises mixing (i) 100 parts by weight of at leastone elastomer containing olefinic unsaturation selected from the groupconsisting of natural rubber and conjugated diene homopolymers andcopolymers and from copolymers of at least one conjugated diene andaromatic vinyl compound; with (ii) 0.05 to 10 parts by weight ofN-(4-hydroxy-phenyl)stearamide. The presence of saidN-(4-hydroxy-phenyl)stearamide in a rubber composition is said toprovide lower minimum Rheometer torque which would indicate less workinput required during Banbury mixing and an improved processingcomposition. Moreover, said stearamide, also improves flex propertiesand abrasion resistance of the crosslinked rubber composition.

U.S. Pat. No. 6,333,375 describes a rubber composition comprising 100part by weight of a diene rubber component, 10 to 200 part by weight ofa reinforcing agent, and 0.1 to 15 parts by weight of a fatty acid salt.Preferably, said fatty acid salt is a metal salt of a fatty acid. Saidrubber composition is said to give a crosslinked rubber compositionhaving an improved heat build-up, tensile strength, abrasion resistanceand processability.

The Applicant has now found that it is possible to obtain crosslinkableelastomeric compositions capable of being used advantageously in theproduction of crosslinked manufactured products, in particular in theproduction of tyre for vehicle wheels, by using a fatty acid amide andat least one zinc salt of a carboxylic acid. In this way, it is possibleto obtain a crosslinkable elastomeric composition which exhibits animproved processability and which gives a crosslinked elastomericmanufactured product endowed with an improved abrasion resistance.Moreover, said properties have been achieved without impairing themechanical properties of said crosslinked manufactured product.

According to a first aspect, the present invention thus relates to atyre for vehicle wheels, comprising at least one structural elementincluding a crosslinked elastomeric material obtained by crosslinking anelastomeric composition comprising:

-   (a) at least one diene elastomeric polymer;-   (b) at least one reinforcing filler;-   (c) from 0.05 phr to 10 phr of zinc oxide;-   (d) from 0.1 phr to 20 phr of at least one fatty acid amide;-   (e) from 0.1 phr to 15 phr of at least one zinc salt of a carboxylic    acid of formula R—COOH, wherein R is selected from linear or    branched C₁-C₂₄ alkyl groups, linear or branched C₂-C₂₄ alkenyl    groups, C₅-C₂₄ cycloalkyl groups, C₆-C₂₄ aryl groups, C₇-C₂₄    alkylaryl or arylalkyl groups.

According to one preferred embodiment, the present invention relates toa tyre for vehicle wheels, comprising:

-   -   a carcass structure with at least one carcass ply shaped in a        substantially toroidal configuration, the opposite lateral edges        of which are associated with respective right-hand and left-hand        bead wires, each bead wire being enclosed in a respective bead;    -   a belt structure comprising at least one belt strip applied in a        circumferentially external position relative to said carcass        structure;    -   a tread band superimposed circumferentially on said belt        structure;    -   a pair of side walls applied laterally on opposite sides        relative to said carcass structure; in which said structural        element which includes said elastomeric composition is the tread        band.

According to a further aspect, the present invention relates to a tyretread band including a crosslinkable elastomeric composition comprising:

-   (a) at least one diene elastomeric polymer;-   (b) at least one reinforcing filler;-   (c) from 0.05 phr to 10 phr of zinc oxide;-   (d) from 0.1 phr to 20 phr of at least one fatty acid amide;-   (e) from 0.1 phr to 15 phr of at least one zinc salt of a carboxylic    acid of formula R—COOH, wherein R is selected from linear or    branched C₁-C₂₄ alkyl groups, linear or branched C₂-C₂₄ alkenyl    groups, C₅-C₂₄ cycloalkyl groups, C₆-C₂₄ aryl groups, C₇-C₂₄    alkylaryl or arylalkyl groups.

For the purposes of the present description and of the claims, the term“phr” means the parts by weight of a given component of the elastomericcomposition per 100 parts by weight of the elastomeric polymer.

According to a further aspect, the present invention relates to anelastomeric composition comprising:

-   (a) at least one diene elastomeric polymer;-   (b) at least one reinforcing filler;-   (c) from 0.05 phr to 10 phr of zinc oxide;-   (d) from 0.1 phr to 20 phr of at least one fatty acid amide;-   (e) from 0.1 phr to 15 phr of at least one zinc salt of a carboxylic    acid of formula R—COOH, wherein R is selected from linear or    branched C₁-C₂₄ alkyl groups, linear or branched C₂-C₂₄ alkenyl    groups, C₅-C₂₄ cycloalkyl groups, C₆-C₂₄ aryl groups, C₇-C₂₄    alkylaryl or arylalkyl groups.

According to a further aspect, the present invention relates to acrosslinked elastomeric manufactured product obtained by crosslinkingthe abovementioned elastomeric composition.

According to one preferred embodiment, the zinc oxide (c) is added tothe elastomeric composition in an amount of from 0.1 phr to 6.0 phr,preferably from 0.5 phr to 5.0 phr.

According to one preferred embodiment, the fatty acid amide (d) is addedto the elastomeric composition in an amount of from 0.5 phr to 10 phr,preferably from 2.0 phr to 6.0 phr.

According to one preferred embodiment, the zinc salt of a carboxylicacid (e) is added to the elastomeric composition in an amount of from0.5 phr to 10 phr, preferably from 1.0 phr to 5.0 phr.

According to one preferred embodiment, the diene elastomeric polymer (a)which may be used in the present invention may be selected from thosecommonly used in sulphur-crosslinkable elastomeric compositions, thatare particularly suitable for producing tyres, that is to say fromelastomeric polymers or copolymers with an unsaturated chain having aglass transition temperature (T_(g)) generally below 20° C., preferablyin the range of from 0° C. to −100° C. These polymers or copolymers maybe of natural origin or may be obtained by solution polymerization,emulsion polymerization or gas-phase polymerization of one or moreconjugated diolefins, optionally blended with at least one comonomerselected from monovinylarenes and/or polar comonomers in an amount ofnot more than 60% by weight.

The conjugated diolefins generally contain from 4 to 12, preferably from4 to 8 carbon atoms, and may be chosen, for example, from the groupcomprising: 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene,1,3-pentadiene, 1,3-hexadiene, 3-butyl-1,3-octadiene,2-phenyl-1,3-butadiene, or mixtures thereof. 1,3-butadiene and isopreneare particularly preferred.

Monovinylarenes which may optionally be used as comonomers generallycontain from 8 to 20, preferably from 8 to 12 carbon atoms, and may bechosen, for example, from: styrene; 1-vinylnaphthalene;2-vinylnaphthalene; various alkyl, cycloalkyl, aryl, alkylaryl orarylalkyl derivatives of styrene such as, for example, α-methylstyrene,3-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene,2-ethyl-4-benzylstyrene, 4-p-tolylstyrene, 4-(4-phenylbutyl)styrene, ormixtures thereof. Styrene is particularly preferred.

Polar comonomers which may optionally be used may be chosen, forexample, from: vinylpyridine, vinylquinoline, acrylic acid andalkylacrylic acid esters, nitriles, or mixtures thereof, such as, forexample, methyl acrylate, ethyl acrylate, methyl methacrylate, ethylmethacrylate, acrylonitrile, or mixtures thereof.

Preferably, the diene elastomeric polymer (a) which may be used in thepresent invention may be chosen, for example, from: cis-1,4-polyisoprene(natural or synthetic, preferably natural rubber), 3,4-polyisoprene,polybutadiene (in particular polybutadiene with a high 1,4-cis content),optionally halogenated isoprene/isobutene copolymers,1,3-butadiene/acrylonitrile copolymers, styrene/1,3-butadienecopolymers, styrene/isoprene/1,3-butadiene copolymers,styrene/1,3-butadiene/acrylonitrile copolymers, or mixtures thereof.

The elastomeric composition according to the present invention mayoptionally comprise at least one elastomeric polymer of one or moremonoolefins with an olefinic comonomer or derivatives thereof (a′). Themonoolefins may be selected from: ethylene and α-olefins generallycontaining from 3 to 12 carbon atoms, such as, for example, propylene,1-butene, 1-pentene, 1-hexene, 1-octene, or mixtures thereof. Thefollowing are preferred: copolymers between ethylene and an α-olefin,optionally with a diene; isobutene homopolymers or copolymers thereofwith small amounts of a diene, which are optionally at least partiallyhalogenated. The diene optionally present generally contains from 4 to20 carbon atoms and is preferably selected from: 1,3-butadiene,isoprene, 1,4-hexadiene, 1,4-cyclohexadiene, 5-ethylidene-2-norbornene,5-methylene-2-norbornene, vinylnorbornene, or mixtures thereof. Amongthese, the following are particularly preferred: ethylene/propylenecopolymers (EPR) or ethylene/propylene/diene copolymers (EPDM);polyisobutene; butyl rubbers; halobutyl rubbers, in particularchlorobutyl or bromobutyl rubbers; or mixtures thereof.

A diene elastomeric polymer (a) or an elastomeric polymer (a′)functionalized by reaction with suitable terminating agents or couplingagents may also be used. In particular, the diene elastomeric polymersobtained by anionic polymerization in the presence of an organometallicinitiator (in particular an organolithium initiator) may befunctionalized by reacting the residual organometallic groups derivedfrom the initiator with suitable terminating agents or coupling agentssuch as, for example, imines, carbodiimides, alkyltin halides,substituted benzophenones, alkoxysilanes or aryloxysilanes (see, forexample, European patent EP 451,604, or patents U.S. Pat. No. 4,742,124and U.S. Pat. No. 4,550,142).

According to one preferred embodiment, the reinforcing filler (b) whichmay be used in the present invention may be selected from those commonlyused for crosslinked manufactured products, in particular in theproduction of tyres, that is to say from carbon black, silica, alumina,aluminosilicates, calcium carbonate, kaolin, or mixtures thereof.

The types of carbon black which may be used according to the presentinvention may be selected from those conventionally used in theproduction of tyres, generally having a surface area of not less than 20m²/g (determined by CTAB absorption as described in ISO standard 6810).

The silica which may be used according to the present invention maygenerally be a pyrogenic silica or, preferably, a precipitated silica,with a BET surface area (measured according to ISO standard 5794/1) offrom 50 m²/g to 500 m²/g, preferably from 70 m²/g to 200 m²/g.

When a reinforcing filler comprising silica is present, the elastomericcomposition may advantageously incorporate a coupling agent capable ofinteracting with the silica and of linking it to the elastomeric baseduring the vulcanization.

Coupling agents that are preferably used are those based on silane whichmay be identified, for example, by the following structural formula (I):(R′)₃Si—C_(n)H_(2n)—X  (I)in which the groups R′, which may be identical or different from eachother, are selected from: alkyl, alkoxy or aryloxy groups or fromhalogen atoms, on condition that at least one of the groups R′ is analkoxy or aryloxy group; n is an integer between 1 and 6 inclusive; X isa group selected from: nitroso, mercapto, amino, epoxide, vinyl, imide,chloro, —(S)_(m)C_(n)H_(2n)—Si—(R)₃ in which m and n are integersbetween 1 and 6 inclusive and the groups R are defined as above.

Among the coupling agents that are particularly preferred arebis(3-triethoxysilylpropyl)tetrasulphide andbis(3-triethoxysilylpropyl)disulphide. Said coupling agents may be usedas such or as a suitable mixture with an inert filler (for examplecarbon black) so as to facilitate their incorporation into theelastomeric composition.

According to one preferred embodiment, said reinforcing filler (b) isadded to the elastomeric composition in an amount of from 0.1 phr to 120phr, preferably from 20 phr to 90 phr.

According to one preferred embodiment, the fatty acid amide (d) whichmay be used in the present invention may be selected from compoundshaving the following formulae (II) or (III):

wherein:

-   -   R₁ and R₄, which may be identical or different from each other,        are selected from linear or branched C₁-C₂₄ alkyl groups, linear        or branched C₂-C₂₄ alkenyl groups, C₅-C₂₄ cycloalkyl groups;    -   R₃ is a linear or branched C₁-C₁₀ alkylene group;    -   R₂ is hydrogen; or is selected from linear or branched C₁-C₂₄        alkyl groups, linear or branched C₂-C₂₄ alkenyl groups, C₅-C₂₄        cycloalkyl groups.

Specific examples of fatty acid amides are: acetamide, propionamide,n-butyramide, n-valeramide, n-caproamide, stearamide, lauroylamide,miristic amide, arachidamide, behenamide, ethylene-bis-stearamide,ethylene-bis-oleamide, or mixtures thereof. Stearamide is particularlypreferred.

The fatty acid amides (d) may be obtained by the reaction of a fattyacid, or its acid chloride or ester, with ammonia or an amine or adiamine. More details relating to said process may be found, forexample, in “Encyclopedia of Chemical Technology”, Kirk-Othmer, ThirdEdition, Vol. 2, John Wiley & Sons, New York, 1978, pages 252-257 and in“Organic Chemistry”, Fieser and Fieser, D.C. Heath and Company, Boston,1944, pages 183-184, 232 and 242.

Examples of fatty acid amides (d) which may be used in the presentinvention and which are currently commercially available are theproducts Crodamides® from Croda.

According to one preferred embodiment, the carboxylic acids of formulaR—COOH may be selected from: C₈-C₁₀ coconout acid, stearic acid, lauricacid, oleic acid, octanoic acid, myristic acid, palmitic acid,palmitoleic acid, linoleic acid, benzoic acid, chlorobenzoic acid,methylbenzoic acid, naphthyl acid.

The zinc salt of a carboxylic acid (e) may be obtained by mixing zincoxide, zinc hydroxide or zinc carbonate with carboxylic acids havingformula R—COOH. This process may be carried out as disclosed, forexample in U.S. Pat. No. 5,302,315.

Examples of zinc salts of carboxylic acids (e) which may be used in thepresent invention and which are currently commercially available are theproducts Polyplastol® 6 from Great Lakes Corp., Aktiplast® PP fromRhein-Chemie, Struktol® A50L or A50P from Schill & Seilacher.

The elastomeric composition according to the present invention may bevulcanized according to known techniques, in particular withsulphur-based vulcanizing systems commonly used for diene elastomericpolymers. To this end, in the composition, after a thermomechanicalworking step, a sulphur-based vulcanizing agent is incorporated togetherwith vulcanization accelerators. During the last mentioned working step,the temperature is generally kept below 120° C. and preferably below100° C., so as to avoid any undesired pre-cross-linking phenomena.

The vulcanizing agent most advantageously used is sulphur, or moleculescontaining sulphur (sulphur donors), with accelerators and activatorsknown to those skilled in the art.

Besides the zinc oxide, other activators may be present in theelastomeric composition according to the present invention. Saidactivators may be selected from fatty acids (e.g. stearic acid) and alsofrom other oxides such as, for example, BiO, PbO, Pb₃O₄, PbO₂, ormixtures thereof.

Accelerators that are commonly used may be selected from:dithiocarbamates, guanidine, thiourea, thiazoles, sulphenamides,thiurams, amines, xanthates, or mixtures thereof.

The elastomeric composition according to the present invention maycomprise other commonly used additives chosen on the basis of thespecific application for which the composition is intended. For example,the following may be added to said composition: antioxidants,anti-ageing agents, plasticizers, adhesives, anti-ozone agents,modifying resins, fibres (for example Kevlar® pulp), or mixturesthereof.

In particular, for the purpose of further improving the processability,a plasticizer generally selected from mineral oils, vegetable oils,synthetic oils, or mixtures thereof, such as, for example, aromatic oil,naphthenic oil, phthalates, soybean oil, or mixtures thereof, may beadded to the elastomeric composition according to the present invention.The amount of plasticizer generally ranges from 2 phr to 100 phr,preferably from 5 phr to 50 phr.

The elastomeric composition according to the present invention may beprepared by mixing together the polymeric components with thereinforcing filler and with the other additives optionally presentaccording to techniques known in the art. The mixing may be carried out,for example, using an open mixer of open-mill type, or an internal mixerof the type with tangential rotors (Banbury) or with interlocking rotors(Intermix), or in continuous mixers of Ko-Kneader type (Buss) or ofco-rotating or counter-rotating twin-screw type or on a two-roll-mill.

The present invention will now be illustrated in further detail by meansof a number of illustrative embodiments, with reference to the attachedFIG. 1, which is a view in cross section of a portion of a tyre madeaccording to the invention.

“a” indicates an axial direction and “r” indicates a radial direction.For simplicity, FIG. 1 shows only a portion of the tyre, the remainingportion not represented being identical and symmetrically arranged withrespect to the radial direction “r”.

The tyre (100) comprises at least one carcass ply (101), the oppositelateral edges of which are associated with respective bead wires (102).The association between the carcass ply (101) and the bead wires 1102)is achieved here by folding back the opposite lateral edges of thecarcass ply (101) around the bead wires (102) so as to form theso-called carcass back-folds (101 a) as shown in FIG. 1.

Alternatively, the conventional bead wires (102) can be replaced with apair of circumferentially inextensible annular inserts formed fromelongate components arranged in concentric coils (not represented inFIG. 1) (see, for example, European patent applications EP 928,680 andEP 928,702). In this case, the carcass ply (101) is not back-foldedaround said annular inserts, the coupling being provided by a secondcarcass ply (not represented in FIG. 1) applied externally over thefirst.

The carcass ply (101) generally consists of a plurality of reinforcingcords arranged parallel to each other and at least partially coated witha layer of elastomeric compound. These reinforcing cords are usuallymade of textile fibres, for example rayon, nylon or polyethyleneterephthalate, or of steel wires stranded together, coated with a metalalloy (for example copper/zinc, zinc/manganese, zinc/molybdenum/cobaltalloys and the like).

The carcass ply (101) is usually of radial type, i.e. it incorporatesreinforcing cords arranged in a substantially perpendicular directionrelative to a circumferential direction. Each bead wire (102) isenclosed in a bead (103), defined along an inner circumferential edge ofthe tyre (100), with which the tyre engages on a rim (not represented inFIG. 1) forming part of a vehicle wheel. The space defined by eachcarcass back-fold (101 a) contains a bead filler (104) in which the beadwires (102) are embedded. An antiabrasive strip (105) is usually placedin an axially external position relative to the carcass back-fold (101a).

A belt structure (106) is applied along the circumference of the carcassply (101). In the particular embodiment in FIG. 1, the belt structure(106) comprises two belt strips (106 a, 106 b) which incorporate aplurality of reinforcing cords, typically metal cords, which areparallel to each other in each strip and intersecting with respect tothe adjacent strip, oriented so as to form a predetermined anglerelative to a circumferential direction. On the radially outermost beltstrip (106 b) may optionally be applied at least one zero-degreereinforcing layer (106 c), commonly known as a “0° belt”, whichgenerally incorporates a plurality of reinforcing cords, typicallytextile cords, arranged at an angle of a few degrees relative to acircumferential direction, and coated and welded together by means of anelastomeric material.

A side wall (108) is also applied externally onto the carcass ply (101),this side wall extending, in an axially external position, from the bead(103) to the end of the belt structure (106).

A tread band (109), whose lateral edges are connected to the side walls(108), is applied circumferentially in a position radially external tothe belt structure (106). Externally, the tread band (109), which can beproduced according to the present invention, has a rolling surface (109a) designed to come into contact with the ground. Circumferentialgrooves which are connected by transverse notches (not represented inFIG. 1) so as to define a plurality of blocks of various shapes andsizes distributed over the rolling surface (109 a) are generally made inthis surface (109 a), which is represented for simplicity in FIG. 1 asbeing smooth.

A strip made of elastomeric material (110), commonly known as a“mini-side wall”, may optionally be present in the connecting zonebetween the side walls (108) and the tread band (109), this mini-sidewall generally being obtained by co-extrusion with the tread band andallowing an improvement in the mechanical interaction between the treadband (109) and the side walls (108). Alternatively, the end portion ofthe side wall (108) directly covers the lateral edge of the tread band(109). A underlayer which forms, with the tread band (109), a structurecommonly known as a “cap and base” (not represented in FIG. 1) mayoptionally be placed between the belt structure (106) and the tread band(109).

A layer of elastomeric material (111) which serves as an “attachmentsheet”, i.e. a sheet capable of providing the connection between thetread band (109) and the belt structure (106), may be placed between thetread band (109) and the belt structure (106).

In the case of tubeless tyres, a rubber layer (112) generally known as a“liner”, which provides the necessary impermeability to the inflationair of the tyre, may also be provided in a radially internal positionrelative to the carcass ply (101).

The process for producing the tyre according to the present inventioncan be carried out according to techniques and using apparatus that areknown in the art, as described, for example, in patents EP 199,064, U.S.Pat. No. 4,872,822, U.S. Pat. No. 4,768,937, said process including atleast one stage of manufacturing the green tyre and at least one stageof vulcanizing this tyre.

More particularly, the process for producing the tyre comprises thestages of preparing, beforehand and separately from each other, a seriesof semi-finished products corresponding to the various parts of the tyre(carcass plies, belt structure, bead wires, fillers, side walls andtread band) which are then combined together using a suitablemanufacturing machine. Next, the subsequent vulcanization stage weldsthe abovementioned semi-finished products together to give a monolithicblock, i.e. the finished tyre.

Naturally, the stage of preparing the abovementioned semi-finishedproducts will be preceded by a stage of preparing and moulding thevarious blends, of which said semi-finished products are made, accordingto conventional techniques.

The green tyre thus obtained is then passed to the subsequent stages ofmoulding and vulcanization. To this end, a vulcanization mould is usedwhich is designed to receive the tyre being processed inside a mouldingcavity having walls which are countermoulded to define the outer surfaceof the tyre when the vulcanization is complete.

Alternative processes for producing a tyre or parts of a tyre withoutusing semi-finished products are disclosed, for example, in theabovementioned patent applications EP 928,680 and EP 928,702.

The green tyre can be moulded by introducing a pressurized fluid intothe space defined by the inner surface of the tyre, so as to press theouter surface of the green tyre against the walls of the mouldingcavity. In one of the moulding methods widely practised, a vulcanizationchamber made of elastomeric material, filled with steam and/or anotherfluid under pressure, is inflated inside the tyre closed inside themoulding cavity. In this way, the green tyre is pushed against the innerwalls of the moulding cavity, thus obtaining the desired moulding.Alternatively, the moulding can be carried out without an inflatablevulcanization chamber, by providing inside the tyre a toroidal metalsupport shaped according to the configuration of the inner surface ofthe tyre to be obtained as decribed, for example, in patent EP 242,840.The difference in coefficient of thermal expansion between the toroidalmetal support and the crude elastomeric material is exploited to achievean adequate moulding pressure.

At this point, the stage of vulcanizing the crude elastomeric materialpresent in the tyre is carried out. To this end, the outer wall of thevulcanization mould is placed in contact with a heating fluid (generallysteam) such that the outer wall reaches a maximum temperature generallyof between 100° C. and 230° C. Simultaneously, the inner surface of thetyre is heated to the vulcanization temperature using the samepressurized fluid used to press the tyre against the walls of themoulding cavity, heated to a maximum temperature of between 100° C. and250° C. The time required to obtain a satisfactory degree ofvulcanization throughout the mass of the elastomeric material can varyin general between 3 min and 90 min and depends mainly on the dimensionsof the tyre. When the vulcanization is complete, the tyre is removedfrom the vulcanization mould.

Although the present invention has been illustrated specifically inrelation to a tyre, other crosslinked elastomeric manufactured productsthat can be produced according to the invention may be, for example,conveyor belts, driving belts or flexible tubes.

The present invention will be further illustrated below by means of anumber of preparation examples, which are given for purely indicativepurposes and without any limitation of this invention.

EXAMPLES 1-4

Preparation of the Elastomeric Compositions

The elastomeric compositions given in Table 1 were prepared as follows(the amounts of the various components are given in phr).

All the ingredients, except for the sulphur, the TBBS and the PVI, weremixed together in an internal mixer of the type with tangential rotors(Banbury) for about 5 min (1^(st) Stage). As soon as the temperaturereached 145±5° C., the elastomeric composition was discharged. Thesulphur, the TBBS and the PVI were then added and mixing was carried outon a two-roll mill (2^(nd) Stage). TABLE 1 EXAMPLES 1 (*) 2 (*) 3 (*) 41^(st) STAGE NR 60.0 60.0 60.0 60.0 BR 40.0 40.0 40.0 40.0 Carbon black55.0 55.0 55.0 55.0 Stearic acid 1.0 1.0 1.0 1.0 Zinc oxide 3.5 3.5 3.53.5 Polyplastol ® 6 — 2.0 — 2.0 Wax 1.0 1.0 1.0 1.0 Aromatic oil 5.0 5.05.0 5.0 Crodamide ® SR — — 2.0 2.0 6PPD 3.0 3.0 3.0 3.0 2^(nd) STAGETBBS 1.7 1.7 1.7 1.7 PVI 0.2 0.2 0.2 0.2 Sulphur 1.2 1.2 1.2 1.2(*) comparative.NR: natural rubber;BR: cis-1,4-polybutadiene (Europrene ® Neocis BR40 - EniChemElastomeri);Carbon black: N115 (Vulcan ® 9 - Cabot);Polyplastol ® 6: mixture of zinc salts of fatty acids (palmitic acid,stearic acid and oleic acid being present in major amount) (Great LakesChemical Corp.);Wax: composition of microcrystalline wax (Antilux ® 654 - Bayer);Crodamide ® SR: stearamide (Croda);6PPD (anti-ageing agent): N-1,3-dimethylbutyl-N′-p-phenylendiamine(Vulkanox ® 4020 - Bayer);TBBS (accelerator): N-t-butyl-2-benzothiazyl-sulphenamide (Vulkacit ®NZ - Bayer);PVI (retardant): N-cyclohexylthiophthalimide (Santogard ® PVI -Monsanto).

The Mooney viscosity ML(1+4) at 100° C. was measured, according to ISOstandard 289/1, on the non-crosslinked compositions obtained asdescribed above. The results obtained are given in Table 2.

The following properties were measured on samples of said elastomericcompositions crosslinked at 170° C. for 10 minutes:

-   -   tensile mechanical properties at 23° C. according to ISO        standard 37 (CA1=stress at 100% elongation; CA3=stress at 300%        elongation; S.B.=stress at break;    -   E.B.=elongation at break);    -   hardness in IHRD degree at 23° C. according to ISO standard 48;    -   rebound at 23° C. according to ISO standard 4662;    -   abraded volume at 23° C. according to DIN standard 53516        expressed as relative volumetric loss with respect to the        reference composition of Example 1 (set at 100).

The results obtained are given in Table 2. TABLE 2 EXAMPLES 1 (*) 2 (*)3 (*) 4 Mooney — 99.80 110.20 89.00 Viscosity (ML1 + 4) CA 1 (MPa) 2.722.74 2.68 2.74 CA 3 (MPa) 13.83 13.68 13.40 13.31 S.B. (MPa) 21.72 21.6821.65 21.61 E.B. (%) 451.50 454.80 468.10 465.80 IRHD hardness 75.2076.00 76.20 77.00 at 23° C. Rebound (%) 49.00 47.00 46.20 46.20 DINabrasion 100 94 115 110 (index)(*): comparative.

The results given in Table 2 show that the elastomeric compositionaccording to the present invention (Example 4) has a lower MooneyViscosity value and, consequently, an improved processability. Moreover,the crosslinked manufactured product obtained from said elastomericcomposition shows a better abrasion resistance. Said results have beenobtained without impairing the mechanical properties of the crosslinkedmanufactured product.

EXAMPLES 5-8

Preparation of the Elastomeric Compositions

The elastomeric compositions given in Table 3 were prepared as follows(the amounts of the various components are given in phr).

All the ingredients, except for the zinc oxide, the sulphur, the 6PPD,the DPG80 and the CBS, were mixed together in an internal mixer of thetype with tangential rotors (Banbury) for about 5 min (1^(st) Stage). Assoon as the temperature reached 145±5° C., the elastomeric compositionwas discharged. Then zinc oxide and 6PPD were added and mixing wascarried out in an internal mixer of the type with tangential rotors(Banbury) for about 4 min (2^(nd) Stage). As soon as the temperaturereached 125±5° C., the elastomeric composition was discharged Then thesulphur, the DPG80 and the CBS were added and mixing was carried out ina two-roll mill (3^(rd) Stage). TABLE 3 EXAMPLES 5 (*) 6 (*) 7 (*) 81^(st) STAGE BR 25.0 25.0 25.0 25.0 SBR 75.0 75.0 75.0 75.0 Silica 65.065.0 65.0 65.0 Silane 10.0 10.0 10.0 10.0 Polyplastol ® 6 — 2.0 — 2.0Crodamide ® SR — — 2.0 2.0 Stearic acid 2.0 2.0 2.0 2.0 Wax 1.0 1.0 1.01.0 Aromatic oil 5.0 5.0 5.0 5.0 2^(nd) STAGE Zinc oxide 2.5 2.5 2.5 2.56PPD 2.0 2.0 2.0 2.0 3^(rd) STAGE DPG80 2.2 2.2 2.2 2.2 CBS 1.6 1.6 1.61.6 Sulphur 1.0 1.0 1.0 1.0(*) comparative.BR: cis-1,4-polybutadiene (Europrene ® Neocis BR40 - EniChemElastomeri);SBR: styrene/butadiene copolymer, obtained by emulsion polymerization,containing 25% by weight of styrene, mixed with 37.5 phr of oil (SBR5025 - Bayer);Silica: precipitated silica (Ultrasil ® VN3 - Degussa);Silane: bis(3-triethoxysilylpropyl)tetrasulphide (product X50Scontaining 50% carbon black and 50% silane - Degussa) (the amounts givenin Table 3 refer only to the silane);Polyplastol ® 6: mixture of zinc salts of fatty acids (palmitic acid,stearic acid and oleic acid being present in major amount) (Great LakesChemical Corp.);Crodamide ® SR: stearamide (Croda);Wax: composition of microcrystalline wax (Antilux ® 654 - Bayer);6PPD (anti-ageing agent): N-1,3-dimethylbutyl-N′-p-phenylendiamine(Vulkanox ® 4020 - Bayer);DPG80 (accelerator): predispersed 80% diphenyl-guanidine (Bayer);CBS (accelerator): N-cyclohexyl-2-benzothiazyl-sulphenamide(Santocure ® - Monsanto).

The Mooney viscosity ML(1+4) at 100° C. was measured, according to ISOstandard 289/1, on the non-crosslinked compositions obtained asdescribed above. The results obtained are given in Table 4.

The following properties were measured on samples of said elastomericcompositions crosslinked at 170° C. for 10 minutes:

-   -   tensile mechanical properties at 23° C. according to ISO        standard 37 (CA1=stress at 100% elongation; CA3=stress at 300%        elongation; S.B.=stress at break; E.B.=elongation at break);    -   hardness in IHRD degree at 23° C. according to ISO standard 48;    -   rebound at 23° C. according to ISO standard 4662;    -   abraded volume at 23° C. according to DIN standard 53516        expressed as relative volumetric loss with respect to the        reference composition of Example 5 (set at 100).

The results obtained are given in Table 4. TABLE 4 EXAMPLES 5 (*) 6 (*)7 (*) 8 Mooney Viscosity 100.50 79.90 95.70 83.30 (ML1 + 4) CA 1 (MPa)2.36 2.30 2.52 2.47 CA 3 (MPa) 11.19 10.59 11.55 11.13 S.B. (MPa) 17.8116.04 16.88 14.49 E.B. (%) 454.50 443.70 432.50 397.00 IRHD hardness76.80 74.50 76.40 74.30 at 23° C. Rebound (%) 34.00 34.00 34.40 33.20DIN abrasion 100 85 105 106 (index)(*): comparative.

The results given in Table 4 show that the elastomeric compositionaccording to the present invention (Example 8) has a lower MooneyViscosity value and, consequently, an improved processability. Moreover,the crosslinked manufactured product obtained from said elastomericcomposition shows a better abrasion resistance. Said results have beenobtained without impairing the mechanical properties of the crosslinkedmanufactured product.

1-44. (canceled)
 45. A tyre for a vehicle wheel, comprising: at leastone structural element including a crosslinked elastomeric materialobtained by crosslinking an elastomeric composition comprising: at leastone diene elastomeric polymer; at least one reinforcing filler; from0.05 phr to 10 phr of zinc oxide; from 0.1 phr to 20 phr of at least onefatty acid amide; and from 0.1 phr to 15 phr of at least one zinc saltof a carboxylic acid of formula R—COOH, wherein R is selected fromlinear or branched C₁-C₂₄ alkyl groups, linear or branched C₂-C₂₄alkenyl groups, C₅-C₂₄ cycloalkyl groups, C₆-C₂₄ aryl groups, C₇-C₂₄alkylaryl or arylalkyl groups.
 46. The tyre of claim 45, comprising: acarcass structure; a belt structure applied in a circumferentiallyexternal position relative to the carcass structure; a tread bandsuperimposed circumferentially on the belt structure; and a pair ofsidewalls applied laterally on opposite sides relative to the carcassstructure; wherein the carcass structure comprises at least one carcassply, wherein the at least one carcass ply is shaped in a substantiallytoroidal configuration, wherein opposite lateral edges of the carcassstructure are associated with respective bead wires, wherein each beadwire is enclosed in a respective bead, wherein the belt structurecomprises at least one belt strip, and wherein the at least onestructural element including the crosslinked elastomeric material is thetread band.
 47. The tyre of claim 45, wherein the elastomericcomposition comprises from 0.1 phr to 6.0 phr of the zinc oxide.
 48. Thetyre of claim 45, wherein the elastomeric composition comprises from 0.5phr to 5.0 phr of the zinc oxide.
 49. The tyre of claim 45, wherein theelastomeric composition comprises from 0.5 phr to 10 phr of the at leastone fatty acid amide.
 50. The tyre of claim 45, wherein the elastomericcomposition comprises from 2.0 phr to 6.0 phr of the at least one fattyacid amide.
 51. The tyre of claim 45, wherein the elastomericcomposition comprises from 0.5 phr to 10 phr of the at least one zincsalt of a carboxylic acid.
 52. The tyre of claim 45, wherein theelastomeric composition comprises from 1.0 phr to 5.0 phr of the atleast one zinc salt of a carboxylic acid.
 53. The tyre of claim 45,wherein the at least one diene elastomeric polymer has a glasstransition temperature (T_(g)) below 20° C.
 54. The tyre of claim 45,wherein the at least one diene elastomeric polymer comprises one or moreof: cis-1,4-polyisoprene; 3,4-polyisoprene; polybutadiene; optionallyhalogenated isoprene/isobutene copolymers; 1,3-butadiene/acrylonitrilecopolymers; styrene/1,3-butadiene copolymers;styrene/isoprene/1,3-butadiene copolymers; andstyrene/1,3-butadiene/acrylonitrile copolymers.
 55. The tyre of claim45, wherein the elastomeric composition further comprises at least oneelastomeric polymer of one or more monoolefins with an olefiniccomonomer or derivatives thereof.
 56. The tyre of claim 54, wherein theat least one elastomeric polymer of one or more monoolefins comprisesone or more of: ethylene/propylene copolymers (EPR) orethylene/propylene/diene copolymers (EPDM); polyisobutene; butylrubbers; and halobutyl rubbers.
 57. The tyre of claim 45, wherein the atleast one reinforcing filler comprises one or more of: carbon black;silica; alumina; aluminosilicates; calcium carbonate; and kaolin. 58.The tyre of claim 45, wherein the at least one reinforcing fillercomprises carbon black.
 59. The tyre of claim 45, wherein the at leastone reinforcing filler comprises silica.
 60. The tyre of claim 45,wherein the elastomeric composition comprises from 0.1 phr to 120 phr ofthe at least one reinforcing filler.
 61. The tyre of claim 45, whereinthe elastomeric composition comprises from 20 phr to 90 phr of the atleast one reinforcing filler.
 62. The tyre of claim 45, wherein the atleast one fatty acid amide is selected from compounds having thefollowing formulae (II) or (III):

wherein R₁ and R₄, which may be identical or different from each other,are selected from linear or branched C₁-C₂₄ alkyl groups, linear orbranched C₂-C₂₄ alkenyl groups, C₅-C₂₄ cycloalkyl groups; wherein R₃ isa linear or branched C₁-C₁₀ alkylene group; and wherein R₂ is hydrogenor is selected from linear or branched C₁-C₂₄ alkyl groups, linear orbranched C₂-C₂₄ alkenyl groups, or C₅-C₂₄ cycloalkyl groups.
 63. Thetyre of claim 62, wherein the at least one fatty acid amide comprisesone or more of: acetamide, propionamide, n-butyramide, n-valeramide,n-caproamide, stearamide, lauroylamide, miristic amide, arachidamide,behenamide, ethylene-bis-stearamide, and ethylene-bis-oleamide.
 64. Thetyre of claim 62, wherein the at least one fatty acid amide comprisesstearamide.
 65. The tyre of claim 45, wherein the carboxylic acid offormula R—COOH comprises one or more of: C₈-C₁₀ coconout acid; stearicacid; lauric acid; oleic acid; octanoic acid; myristic acid; palmiticacid; palmitoleic acid; linoleic acid; benzoic acid; chlorobenzoic acid;methylbenzoic acid; and naphthyl acid.
 66. A tyre tread band including acrosslinkable elastomeric composition, the composition comprising: atleast one diene elastomeric polymer; at least one reinforcing filler;from 0.05 phr to 10 phr of zinc oxide; from 0.1 phr to 20 phr of atleast one fatty acid amide; and from 0.1 phr to 15 phr of at least onezinc salt of a carboxylic acid of formula R—COOH, wherein R is selectedfrom linear or branched C₁-C₂₄ alkyl groups, linear or branched C₂-C₂₄alkenyl groups, C₅-C₂₄ cycloalkyl groups, C₆-C₂₄ aryl groups, C₇-C₂₄alkylaryl or arylalkyl groups.
 67. The tyre tread band of claim 66,wherein the elastomeric composition comprises from 0.1 phr to 6.0 phr ofthe zinc oxide.
 68. The tyre tread band of claim 66, wherein the zincoxide (c) is added to the elastomeric composition in an amount of from0.5 phr to 5.0 phr.
 69. The tyre tread band of claim 66, wherein theelastomeric composition comprises from 0.5 phr to 10 phr of the at leastone fatty acid amide.
 70. The tyre tread band of claim 66, wherein theelastomeric composition comprises from 2.0 phr to 6.0 phr of the atleast one fatty acid amide.
 71. The tyre tread band of claim 66, whereinthe elastomeric composition comprises from 0.5 phr to 10 phr of the atleast one zinc salt of a carboxylic acid.
 72. The tyre tread band ofclaim 66, wherein the elastomeric composition comprises from 1.0 phr to5.0 phr of the at least one zinc salt of a carboxylic acid.
 73. The tyretread band of claim 66, wherein the at least one diene elastomericpolymer comprises one or more of: cis-1,4-polyisoprene;3,4-polyisoprene; polybutadiene; optionally halogenatedisoprene/isobutene copolymers; 1,3-butadiene/acrylonitrile copolymers;styrene/1,3-butadiene copolymers; styrene/isoprene/1,3-butadienecopolymers; and styrene/1,3-butadiene/acrylonitrile copolymers.
 74. Thetyre tread band of claim 66, wherein the at least one reinforcing fillercomprises one or more of: carbon black; silica; alumina;aluminosilicates; calcium carbonate; and kaolin.
 75. The tyre tread bandof claim 66, wherein the at least one fatty acid amide is selected fromcompounds having the following formulae (II) or (III):

wherein R₁ and R₄, which may be identical or different from each other,are selected from linear or branched C₁-C₂₄ alkyl groups, linear orbranched C₂-C₂₄ alkenyl groups, C₅-C₂₄ cycloalkyl groups; wherein R₃ isa linear or branched C₁-C₁₀ alkylene group; and wherein R₂ is hydrogenor is selected from linear or branched C₁-C₂₄ alkyl groups, linear orbranched C₂-C₂₄ alkenyl groups, or C₅-C₂₄ cycloalkyl groups.
 76. Thetyre tread band of claim 66, wherein the carboxylic acid of formulaR—COOH comprises one or more of: C₈-C₁₀ coconout acid; stearic acid;lauric acid; oleic acid; octanoic acid; myristic acid; palmitic acid;palmitoleic acid; linoleic acid; benzoic acid; chlorobenzoic acid;methylbenzoic acid; and naphthyl acid.
 77. An elastomeric composition,comprising: at least one diene elastomeric polymer; at least onereinforcing filler; from 0.05 phr to 10 phr of zinc oxide; from 0.1 phrto 20 phr of at least one fatty acid amide; and from 0.1 phr to 15 phrof at least one zinc salt of a carboxylic acid of formula R—COOH,wherein R is selected from linear or branched C₁-C₂₄ alkyl groups,linear or branched C₂-C₂₄ alkenyl groups, C₅-C₂₄ cycloalkyl groups,C₆-C₂₄ aryl groups, C₇-C₂₄ alkylaryl or arylalkyl groups.
 78. Theelastomeric composition of claim 77, comprising from 0.1 phr to 6.0 phrof the zinc oxide.
 79. The elastomeric composition of claim 77,comprising from 0.5 phr to 5.0 phr of the zinc oxide.
 80. Theelastomeric composition of claim 77, comprising from 0.5 phr to 10 phrof the at least one fatty acid amide.
 81. The elastomeric composition ofclaim 77, comprising from 2.0 phr to 6.0 phr of the at least one fattyacid amide.
 82. The elastomeric composition of claim 77, comprising from0.5 phr to 10 phr of the at least one zinc salt of a carboxylic acid.83. The elastomeric composition of claim 77, comprising from 1.0 phr to5.0 phr of the at least one zinc salt of a carboxylic acid.
 84. Theelastomeric composition of claim 77, wherein the at least one dieneelastomeric polymer comprises one or more of: cis-1,4-polyisoprene;3,4-polyisoprene; polybutadiene; optionally halogenatedisoprene/isobutene copolymers; 1,3-butadiene/acrylonitrile copolymers;styrene/1,3-butadiene copolymers; styrene/isoprene/1,3-butadienecopolymers; and styrene/1,3-butadiene/acrylonitrile copolymers.
 85. Theelastomeric composition of claim 77, wherein the at least onereinforcing filler comprises one or more of: carbon black; silica;alumina; aluminosilicates; calcium carbonate; and kaolin.
 86. Theelastomeric composition of claim 77, wherein the at least one fatty acidamide is selected from compounds having the following formulae (II) or(III):

wherein R₁ and R₄, which may be identical or different from each other,are selected from linear or branched C₁-C₂₄ alkyl groups, linear orbranched C₂-C₂₄ alkenyl groups, C₅-C₂₄ cycloalkyl groups; wherein R₃ isa linear or branched C₁-C₁₀ alkylene group; and wherein R₂ is hydrogenor is selected from linear or branched C₁-C₂₄ alkyl groups, linear orbranched C₂-C₂₄ alkenyl groups, or C₅-C₂₄ cycloalkyl groups.
 87. Theelastomeric composition of claim 77, wherein the carboxylic acid offormula R—COOH comprises one or more of: C₈-C₁₀ coconout acid; stearicacid; lauric acid; oleic acid; octanoic acid; myristic acid; palmiticacid; palmitoleic acid; linoleic acid; benzoic acid; chlorobenzoic acid;methylbenzoic acid; and naphthyl acid.
 88. A crosslinked elastomericmanufactured product obtained by crosslinking the elastomericcomposition of claim 77.